M. tuberculosis induction of matrix metalloproteinase-9: the role of mannose and receptor-mediated mechanisms

Breaking the Cycle: Matrix Metalloproteinase Inhibitors as an Alternative Approach in Managing Tuberculosis Pathogenesis and Progression

Mycobacterium tuberculosis (Mtb) has long posed a significant challenge to global public health, resulting in approximately 1.6 million deaths annually. Pulmonary tuberculosis (TB) instigated by Mtb is characterized by extensive lung tissue damage, leading to lesions and dissemination within the tissue matrix. Matrix metalloproteinases (MMPs) exhibit endopeptidase activity, contributing to inflammatory tissue damage and, consequently, morbidity and mortality in TB patients. MMP activities in TB are intricately regulated by various components, including cytokines, chemokines, cell receptors, and growth factors, through intracellular signaling pathways. Primarily, Mtb-infected macrophages induce MMP expression, disrupting the balance between MMPs and tissue inhibitors of metalloproteinases (TIMPs), thereby impairing extracellular matrix (ECM) deposition in the lungs. Recent research underscores the significance of immunomodulatory factors in MMP secretion and granuloma formation during Mtb pathogenesis. Several studies have investigated both the activation and inhibition of MMPs using endogenous MMP inhibitors (i.e., TIMPs) and synthetic inhibitors. However, despite their promising pharmacological potential, few MMP inhibitors have been explored for TB treatment as host-directed therapy. Scientists are exploring novel strategies to enhance TB therapeutic regimens by suppressing MMP activity to mitigate Mtb-associated matrix destruction and reduce TB induced lung inflammation. These strategies include the use of MMP inhibitor molecules alone or in combination with anti-TB drugs. Additionally, there is growing interest in developing novel formulations containing MMP inhibitors or MMP-responsive drug delivery systems to suppress MMPs and release drugs at specific target sites. This review summarizes MMPs' expression and regulation in TB, their role in immune response, and the potential of MMP inhibitors as effective therapeutic targets to alleviate TB immunopathology.

Mycobacterium tuberculosis and host interactions in the manifestation of tuberculosis

The final step of epigenetic processes is changing the gene expression in a new microenvironment in the body, such as neuroendocrine changes, active infections, oncogenes, or chemical agents. The case of tuberculosis (TB) is an outcome of Mycobacterium tuberculosis (M.tb) and host interaction in the manifestation of active and latent TB or clearance. This comprehensive review explains and interprets the epigenetics findings regarding gene expressions on the host-pathogen interactions in the development and progression of tuberculosis. This review introduces novel insights into the complicated host-pathogen interactions, discusses the challengeable results, and shows the gaps in the clear understanding of M.tb behavior. Focusing on the biological phenomena of host-pathogen interactions, the epigenetic changes, and their outcomes provides a promising future for developing effective TB immunotherapies when converting gene expression toward appropriate host immune responses gradually becomes attainable. Overall, this review may shed light on the dark sides of TB pathogenesis as a life-threatening disease. Therefore, it may support effective planning and implementation of epigenetics approaches for introducing proper therapies or effective vaccines.

Proteomic analysis of granulomas from cattle and pigs naturally infected with Mycobacterium tuberculosis complex by MALDI imaging

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) has recently gained prominence for its ability to provide molecular and spatial information in tissue sections. This technology has the potential to uncover novel insights into proteins and other molecules in biological and immunological pathways activated along diseases with a complex host-pathogen interaction, such as animal tuberculosis. Thus, the present study conducted a data analysis of protein signature in granulomas of cattle and pigs naturally infected with the Mycobacterium tuberculosis complex (MTC), identifying biological and immunological signaling pathways activated throughout the disease. Lymph nodes from four pigs and four cattle, positive for the MTC by bacteriological culture and/or real-time PCR, were processed for histopathological examination and MALDI-MSI. Protein identities were assigned using the MaTisse database, and protein-protein interaction networks were visualized using the STRING database. Gene Ontology (GO) analysis was carried out to determine biological and immunological signaling pathways in which these proteins could participate together with Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Distinct proteomic profiles between cattle and pig granulomas were displayed. Noteworthy, the GO analysis revealed also common pathways among both species, such as "Complement activation, alternative pathway" and "Tricarboxylic acid cycle", which highlight pathways that are conserved among different species infected by the MTC. In addition, species-specific terms were identified in the current study, such as "Natural killer cell degranulation" in cattle or those related to platelet and neutrophil recruitment and activation in pigs. Overall, this study provides insights into the immunopathogenesis of tuberculosis in cattle and pigs, opening new areas of research and highlighting the importance, among others, of the complement activation pathway and the regulation of natural killer cell- and neutrophil-mediated immunity in this disease.

Gene Expression Study of Host and Mycobacterium tuberculosis Interactions in the Manifestation of Acute Tuberculosis

Mycobacterium tuberculosis (M.tb) could induce type IV hypersensitivity. The chemotaxis of the leukocytes toward the site of infection and producing matrix metalloproteinases (MMPs) are key factors in the immune pathogenesis of tuberculosis (TB). Mononuclear cells were isolated from bronchoalveolar lavage (BAL) specimens, and the target from genomic DNA was used for qPCR TB diagnosis and cDNA for specific RT-qPCR gene expression. The subjects were then classified into TB⁺ and TB^- groups, and the expression levels of CFP-10, ESAT-6, CCR1, CCR12 and MMP3,9 were evaluated. The mean level of CCR1 expression in TB⁺ and TB^- patients' BAL was 1.71 ± 0.78 and 0.5 ± 0.22, respectively, which was statistically different (p = 0.01). The CCR2 level, in TB⁺ (2.07 ± 1.4), was higher than in TB^- patients (1.42 ± 0.89, p = 0.01). The MMP9 expression in TB⁺ was 2.56 ± 0.68, also higher than in TB^- patients (1.13 ± 0.35), while MMP3 was lower in TB⁺ (0.22 ± 0.09) than in TB^- (0.64 ± 0.230, p = 0.05). The CCR2/CCR1 and MMP3/MMP9 balance in TB⁺ were reduced, compared to the TB^-. The CFP-10 and ESAT-6 were highly expressed in TB⁺ patients. The CFP-10 expression had a strong negative correlation with albumin (r =  - 0.93, p = 0.001), and a negative correlation with neutrophil (r =  - 0.444, p = 0.1 with 90% CI). The MMP-9 expression showed a positive correlation with WBC count (r = 0.61, p = 0.02), in TB⁺, and had a negative correlation with BMI (r = 0.59, p = 0.02) in TB^-. The M.tb CFP-10 might be implicated in lowering CCR2 and MMP3 expression in favour of M.tb dissemination. Moreover, the balance of CCR2/CCR1 and MMP3/MMP9 can be used as prognostic factors in the severity of TB.

KLK12 Regulates MMP-1 and MMP-9 via Bradykinin Receptors: Biomarkers for Differentiating Latent and Active Bovine Tuberculosis

It has been established that kallikrein12 (KLK12) expression is closely related to bovine tuberculosis (bTB) development. Herein, we sought to clarify the regulatory mechanism of KLK12 and its application in tuberculosis diagnosis. KLK12 knockdown macrophages were produced by siRNA transfection. Bradykinin receptors (BR, including B1R and B2R) were blocked with specific inhibitors. Mannose-capped lipoarabinomannan (ManLAM) was extracted from Mycobacterium bovis (M. bovis) and used to study the mechanism of KLK12 activation. In addition, we constructed different mouse models representing the latent and active stages of M. bovis infection. Mouse models and clinical serum samples were used to assess the diagnostic value of biomarkers. Through the above methods, we confirmed that KLK12 regulates MMP-1 and MMP-9 via BR. KLK12 upregulation is mediated by the M. bovis-specific antigen ManLAM. KLK12, MMP-1, and MMP-9 harbor significant value as serological markers for differentiating between latent and active bTB, especially KLK12. In conclusion, we identified a novel signaling pathway, KLK12/BR/ERK/MMPs, in M. bovis-infected macrophages, which is activated by ManLAM. From this signaling pathway, KLK12 can be used as a serological marker to differentiate between latent and active bTB. Importantly, KLK12 also has enormous potential for the clinical diagnosis of human tuberculosis (TB).

Sensing of mycobacterial arabinogalactan by galectin-9 exacerbates mycobacterial infection

Mycobacterial arabinogalactan (AG) is an essential cell wall component of mycobacteria and a frequent structural and bio-synthetical target for anti-tuberculosis (TB) drug development. Here, we report that mycobacterial AG is recognized by galectin-9 and exacerbates mycobacterial infection. Administration of AG-specific aptamers inhibits cellular infiltration caused by Mycobacterium tuberculosis (Mtb) or Mycobacterium bovis BCG, and moderately increases survival of Mtb-infected mice or Mycobacterium marinum-infected zebrafish. AG interacts with carbohydrate recognition domain (CRD) 2 of galectin-9 with high affinity, and galectin-9 associates with transforming growth factor β-activated kinase 1 (TAK1) via CRD2 to trigger subsequent activation of extracellular signal-regulated kinase (ERK) as well as induction of the expression of matrix metalloproteinases (MMPs). Moreover, deletion of galectin-9 or inhibition of MMPs blocks AG-induced pathological impairments in the lung, and the AG-galectin-9 axis aggravates the process of Mtb infection in mice. These results demonstrate that AG is an important virulence factor of mycobacteria and galectin-9 is a novel receptor for Mtb and other mycobacteria, paving the way for the development of novel effective TB immune modulators.

Innate Immune Pattern Recognition Receptors of Mycobacterium tuberculosis: Nature and Consequences for Pathogenesis of Tuberculosis

Innate immunity against Mycobacterium tuberculosis is a critical early response to prevent the establishment of the infection. Despite recent advances in understanding the host-pathogen dialogue in the early stages of tuberculosis (TB), much has yet to be learnt. The nature and consequences of this dialogue ultimately determine the path of infection: namely, either early clearance of M. tuberculosis, or establishment of M. tuberculosis infection leading to active TB disease and/or latent TB infection. On the frontline in innate immunity are pattern recognition receptors (PRRs), with soluble factors (e.g. collectins and complement) and cell surface factors (e.g. Toll-like receptors and other C-type lectin receptors (Dectin 1/2, Nod-like receptors, DC-SIGN, Mincle, mannose receptor, and MCL) that play a central role in recognising M. tuberculosis and facilitating its clearance. However, in a 'double-edged sword' scenario, these factors can also be involved in enhancement of pathogenesis as well. Furthermore, innate immunity is also a critical bridge in establishing the subsequent adaptive immune response, which is also responsible for granuloma formation that cordons off M. tuberculosis infection, establishing latency and acting as a reservoir for bacterial persistence and dissemination of future disease. This chapter discusses the current understanding of pattern recognition of M. tuberculosis by innate immunity and the role this plays in the pathogenesis and protection against TB.

Matrix metalloproteinases: Expression, regulation and role in the immunopathology of tuberculosis

Mycobacterium tuberculosis (Mtb) leads to approximately 1.5 million human deaths every year. In pulmonary tuberculosis (TB), Mtb must drive host tissue destruction to cause pulmonary cavitation and dissemination in the tissues. Matrix metalloproteinases (MMPs) are endopeptidases capable of degrading all components of pulmonary extracellular matrix (ECM). It is well established that Mtb infection leads to upregulation of MMPs and also causes disturbance in the balance between MMPs and tissue inhibitors of metalloproteinases (TIMPs), thus altering the extracellular matrix deposition. In TB, secretion of MMPs is mainly regulated by NF-κB, p38 and MAPK signalling pathways. In addition, recent studies have demonstrated the immunomodulatory roles of MMPs in Mtb pathogenesis. Researchers have proposed a new regimen of improved TB treatment by inhibition of MMP activity to hinder matrix destruction and to minimize the TB-associated morbidity and mortality. The proposed regimen involves adjunctive use of MMP inhibitors such as doxycycline, marimastat and other related drugs along with front-line anti-TB drugs to reduce granuloma formation and bacterial load. These findings implicate the possible addition of economical and well-tolerated MMP inhibitors to current multidrug regimens as an attractive mean to increase the drug potency. Here, we will summarize the recent advancements regarding expression of MMPs in TB, their immunomodulatory role, as well as their potential as therapeutic targets to control the deadly disease.

Role of apoptosis and autophagy in tuberculosis

Tuberculosis (TB) is one of the oldest known human diseases and is transmitted by the bacteria Mycobacterium tuberculosis (Mtb). TB has a rich history with evidence of TB infections dating back to 5,800 bc TB is unique in its ability to remain latent in an individual for decades, with the possibility of later reactivation, causing widespread systemic symptoms. Currently, it is estimated that more than one-third of the world's population (~2 billion people) are infected with Mtb. Prolonged periods of therapy and complexity of treatment regimens, especially in active infection, have led to poor compliance in patients being treated for TB. Therefore, it is vitally important to have a thorough knowledge of the pathophysiology of Mtb to understand the disease progression, as well as to develop novel diagnostic tests and treatments. Alveolar macrophages represent both the primary host cell and the first line of defense against the Mtb infection. Apoptosis and autophagy of macrophages play a vital role in the pathogenesis and also in the host defense against Mtb. This review will outline the role of these two cellular processes in defense against Mtb with particular emphasis on innate immunity and explore developing therapies aimed at altering host responses to the disease.

Modulation of Macrophage Responses by CMX, a Fusion Protein Composed of Ag85c, MPT51, and HspX from Mycobacterium tuberculosis

Mycobacterium bovis Bacillus Calmette–Guérin (BCG) is a vaccine used to prevent tuberculosis (TB). Due to the poor protection conferred by BCG in adults, new, more effective formulations have been developed. A recombinant BCG vaccine expressing the CMX fusion protein Ag85c_MPT51_HspX (rBCG-CMX) induced Th1 and Th17 responses and provided better protection than BCG. It has been shown that Mycobacterium smegmatis expressing CMX also induces better protection than BCG and is a strong macrophage activator. The aim of the present study was to evaluate macrophage activation by the recombinant CMX fusion protein and by rBCG-CMX and to evaluate their ability to generate vaccine-specific immune responses. The results demonstrate that rCMX protein expressed by BCG (rBCG-CMX) activates pulmonary macrophages; increases the expression of activation molecules, cytokines, and MHC-II. The interaction with rCMX activates the transcription factor NF-κB and induces the production of the cytokines TGF-β, TNF-α, and IL-6. The in vitro stimulation of bone marrow-derived macrophages (BMMs) from TLR-4 or TLR-2 KO mice showed that in the absence of TLR-4, IL-6 was not produced. rBCG-CMX was unable to induce CMX-specific Th1 and Th17 cells in TLR-4 and TLR-2 KO mice, suggesting that these receptors participate in their induction. We concluded that both the rBCG-CMX vaccine and the rCMX protein can activate macrophages and favor the specific immune response necessary for this vaccine.

Title: role of matrix metalloproteinase -9 in progression of tuberculous meningitis: a pilot study in patients at different stages of the disease

BACKGROUND

TBM (Tuberculous meningitis) is severe form of tuberculosis causing death of one third of the affected individuals or leaving two-third of the survivors disabled. MMP-9 (Matrix metalloproteinase-9) is produced by the central nervous system in a variety of inflammatory conditions and has a role in the breakdown of extracellular matrix and blood-brain barrier.

METHODS

In this study, the levels of MMP-9 and its inhibitor, TIMP-1 (tissue inhibitor of metalloproteinases-1), were screened using zymography and reverse zymography in cerebrospinal fluid and serum of tuberculous meningitis patients at different stages of the disease. Further, role of MMP-9 as therapeutic target was studied in C6 glioma cells infected with Mycobacterium tuberculosis H₃₇R_v. Cells were treated with dexamethasone or SB-3CT (specific inhibitor of MMP-9) in combination with conventional antitubercular drugs.

RESULTS

MMP-9 levels in patients were increased as the disease progressed to advanced stages. The infection led to increased MMP-9 levels in C6 glioma cells and specific inhibition of MMP-9 by SB-3CT augmented bacillary clearance when used along with antitubercular drugs.

CONCLUSION

MMP-9 plays a prominent role in progression of tuberculous meningitis from initial to advanced stages. Increased levels of MMP-9 during advancement of the disease leads to degeneration of nervous tissue and blood brain barrier disruption. Hence, MMP-9 can be considered as a therapeutic target for efficient management of TBM and can be explored to inhibit further progression of the disease if used at an early stage.

Adjunctive role of MMP-9 inhibition along with conventional anti-tubercular drugs against experimental tuberculous meningitis

Tuberculous meningitis (TBM) is an outcome of neuroinflammatory degeneration caused due to Mycobacterium tuberculosis infection and leads to death or neurological disabilities in the affected individuals. It causes the highest morbidity and mortality amongst all forms of tuberculosis. Matrix metalloproteinase-9 levels increase and cause inflammatory destruction during progression of the disease. Although corticosteroids are usually given as an adjuvant therapy to overcome these complications, treatment outcome is contradictory. This study was designed to evaluate whether specific inhibition of MMP-9 can be beneficial in management of the disease. MMP-9 levels were inhibited using SB-3CT or dexamethasone along with conventional drugs for treatment of tuberculous meningitis. Both SB-3CT and dexamethasone decreased the elevated levels of MMP-9 in sera and tissues of the infected mice. However, dexamethasone administration had an inhibitory effect on bacillary clearance, while SB-3CT potentiated the bacillary clearance, suggesting that MMP-9, if specifically inhibited, can be beneficial in the management of TBM.

Expression kinetics of metalloproteinases and their tissue inhibitors in experimental murine pulmonary tuberculosis

AIM

Explore the temporal expression of metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) during experimental tuberculosis induced by virulent Mycobacterium tuberculosis strain H37Rv.

METHODS

BALB/c mice were infected via endotracheal instillation with H37Rv. Groups of mice were euthanized at different time points during infection. RNA was isolated from the lungs, and the expression of MMP-3, 8, 9, 10, 12, 13 and TIMP-1-4 was determined by quantitative PCR. Immunohistochemical detection of MMP-3, MMP-9, and MMP-10 was done to determine the cell source.

RESULTS

The infection with H37Rv-induced inflammation resulted in maximal up-regulation of MMP-3, 8, 9, 10, 12 and 13 at day 21 postinfection. Additionally, MMP-13 showed another expression peak during late disease at day 60. Airway epithelium and macrophages were the most common MMP-3 and MMP-9 immunopositive cells, while for MMP-10, macrophages and endothelial cells were the most common, particularly at days 14 and 21 in well-formed granulomas. During late disease, vacuolated macrophages in pneumonic areas and bronchial epithelium showed mild MMP immunostaining.

CONCLUSIONS

MMP-3, 8, 9, 10, 12, and 13 are maximally expressed at the peak of granuloma formation in the mouse tuberculosis model, with no compensation in levels or timing of TIMP expression. This data opens the possibility of participation of these molecules in the granuloma process.

Macrophages in tuberculosis: friend or foe

Tuberculosis (TB) remains one of the greatest threats to human health. The causative bacterium, Mycobacterium tuberculosis (Mtb), is acquired by the respiratory route. It is exquisitely human adapted and a prototypic intracellular pathogen of macrophages, with alveolar macrophages (AMs) being the primary conduit of infection and disease. The outcome of primary infection is most often a latently infected healthy human host, in whom the bacteria are held in check by the host immune response. Such individuals can develop active TB later in life with impairment in the immune system. In contrast, in a minority of infected individuals, the host immune response fails to control the growth of bacilli, and progressive granulomatous disease develops, facilitating spread of the bacilli via infectious aerosols coughed out into the environment and inhaled by new hosts. The molecular details of the Mtb-macrophage interaction continue to be elucidated. However, it is clear that a number of complex processes are involved at the different stages of infection that may benefit either the bacterium or the host. Macrophages demonstrate tremendous phenotypic heterogeneity and functional plasticity which, depending on the site and stage of infection, facilitate the diverse outcomes. Moreover, host responses vary depending on the specific characteristics of the infecting Mtb strain. In this chapter, we describe a contemporary view of the behavior of AMs and their interaction with various Mtb strains in generating unique immunologic lung-specific responses.

ACE/ACE2 ratio and MMP-9 activity as potential biomarkers in tuberculous pleural effusions

OBJECTIVE

Pleural effusion is common problem, but the rapid and reliable diagnosis for specific pathogenic effusions are lacking. This study aimed to identify the diagnosis based on clinical variables to differentiate pleural tuberculous exudates from other pleural effusions. We also investigated the role of renin-angiotensin system (RAS) and matrix metalloproteinase (MMPs) in the pathogenesis of pleural exudates.

EXPERIMENTAL DESIGN

The major components in RAS and extracellular matrix metabolism, including angiotensin converting enzyme (ACE), ACE2, MMP-2 and MMP-9 activities, were measured and compared in the patients with transudative (n = 45) and exudative (n = 80) effusions. The exudative effusions were come from the patients with tuberculosis (n = 20), pneumonia (n = 32), and adenocarcinoma (n = 28).

RESULTS

Increased ACE and equivalent ACE2 activities, resulting in a significantly increased ACE/ACE2 ratio in exudates, were detected compared to these values in transudates. MMP-9 activity in exudates was significantly higher than that in transudates. The significant correlation between ACE and ACE2 activity that was found in transudates was not found in exudates. Advanced analyses showed significantly increased ACE and MMP-9 activities, and decreased ACE2 activity in tuberculous pleural effusions compared with those in pneumonia and adenocarcinoma effusions. The results indicate that increased ACE and MMP-9 activities found in the exudates were mainly contributed from a higher level of both enzyme activities in the tuberculous pleural effusions.

CONCLUSION

Interplay between ACE and ACE2, essential functions in the RAS, and abnormal regulation of MMP-9 probably play a pivotal role in the development of exudative effusions. Moreover, the ACE/ACE2 ratio combined with MMP-9 activity in pleural fluid may be potential biomarkers for diagnosing tuberculous pleurisy.

Matrix metalloproteinase proteolysis of the mycobacterial HSP65 protein as a potential source of immunogenic peptides in human tuberculosis

Mycobacterium tuberculosis is the causative agent of human tuberculosis (TB). Mycobacterial secretory protein ESAT-6 induces matrix metalloproteinase (MMP)-9 in epithelial cells neighboring infected macrophages. MMP-9 then enhances recruitment of uninfected macrophages, which contribute to nascent granuloma maturation and bacterial growth. Disruption of MMP-9 function attenuates granuloma formation and bacterial growth. The abundant mycobacterial 65 kDa heat shock protein (HSP65) chaperone is the major target for the immune response and a critical component in M. tuberculosis adhesion to macrophages. We hypothesized that HSP65 is susceptible to MMP-9 proteolysis and that the resulting HSP65 immunogenic peptides affect host adaptive immunity. To identify MMPs that cleave HSP65, we used MMP-2 and MMP-9 gelatinases, the simple hemopexin domain MMP-8, membrane-associated MMP-14, MMP-15, MMP-16 and MMP-24, and glycosylphosphatidylinositol-linked MMP-17 and MMP-25. We determined both the relative cleavage efficiency of MMPs against the HSP65 substrate and the peptide sequence of the cleavage sites. Cleavage of the unstructured PAGHG474L C-terminal region initiates the degradation of HSP65 by MMPs. This initial cleavage destroys the substrate-binding capacity of the HSP65 chaperone. Multiple additional cleavages of the unfolded HSP65 then follow. MMP-2, MMP-8, MMP-14, MMP-15 and MMP-16, in addition to MMP-9, generate the known highly immunogenic N-terminal peptide of HSP65. Based on our biochemical data, we now suspect that MMP proteolysis of HSP65 in vivo, including MMP-9 proteolysis, also results in the abundant generation of the N-terminal immunogenic peptide and that this peptide, in addition to intact HSP65, contributes to the complex immunomodulatory interplay in the course of TB infection.

Lipoarabinomannan and related glycoconjugates: structure, biogenesis and role in Mycobacterium tuberculosis physiology and host-pathogen interaction

Approximately one third of the world's population is infected with Mycobacterium tuberculosis, the causative agent of tuberculosis. This bacterium has an unusual lipid-rich cell wall containing a vast repertoire of antigens, providing a hydrophobic impermeable barrier against chemical drugs, thus representing an attractive target for vaccine and drug development. Apart from the mycolyl–arabinogalactan–peptidoglycan complex, mycobacteria possess several immunomodulatory constituents, notably lipomannan and lipoarabinomannan. The availability of whole-genome sequences of M. tuberculosis and related bacilli over the past decade has led to the identification and functional characterization of various enzymes and the potential drug targets involved in the biosynthesis of these glycoconjugates. Both lipomannan and lipoarabinomannan possess highly variable chemical structures, which interact with different receptors of the immune system during host–pathogen interactions, such as Toll-like receptors-2 and C-type lectins. Recently, the availability of mutants defective in the synthesis of these glycoconjugates in mycobacteria and the closely related bacterium, Corynebacterium glutamicum, has paved the way for host–pathogen interaction studies, as well as, providing attenuated strains of mycobacteria for the development of new vaccine candidates. This review provides a comprehensive account of the structure, biosynthesis and immunomodulatory properties of these important glycoconjugates.

Surfactant protein A (SP-A)-mediated clearance of Staphylococcus aureus involves binding of SP-A to the staphylococcal adhesin eap and the macrophage receptors SP-A receptor 210 and scavenger receptor class A

Staphylococcus aureus causes life-threatening pneumonia in hospitals and deadly superinfection during viral influenza. The current study investigated the role of surfactant protein A (SP-A) in opsonization and clearance of S. aureus. Previous studies showed that SP-A mediates phagocytosis via the SP-A receptor 210 (SP-R210). Here, we show that SP-R210 mediates binding and control of SP-A-opsonized S. aureus by macrophages. We determined that SP-A binds S. aureus through the extracellular adhesin Eap. Consequently, SP-A enhanced macrophage uptake of Eap-expressing (Eap(+)) but not Eap-deficient (Eap(-)) S. aureus. In a reciprocal fashion, SP-A failed to enhance uptake of Eap(+) S. aureus in peritoneal Raw264.7 macrophages with a dominant negative mutation (SP-R210(DN)) blocking surface expression of SP-R210. Accordingly, WT mice cleared infection with Eap(+) but succumbed to sublethal infection with Eap- S. aureus. However, SP-R210(DN) cells compensated by increasing non-opsonic phagocytosis of Eap(+) S. aureus via the scavenger receptor scavenger receptor class A (SR-A), while non-opsonic uptake of Eap(-) S. aureus was impaired. Macrophages express two isoforms: SP-R210(L) and SP-R210(S). The results show that WT alveolar macrophages are distinguished by expression of SP-R210(L), whereas SR-A(-/-) alveolar macrophages are deficient in SP-R210(L) expressing only SP-R210(S). Accordingly, SR-A(-/-) mice were highly susceptible to both Eap(+) and Eap(-) S. aureus. The lungs of susceptible mice generated abnormal inflammatory responses that were associated with impaired killing and persistence of S. aureus infection in the lung. In conclusion, alveolar macrophage SP-R210(L) mediates recognition and killing of SP-A-opsonized S. aureus in vivo, coordinating inflammatory responses and resolution of S. aureus pneumonia through interaction with SR-A.

Non-acylated Mycobacterium bovis glycoprotein MPB83 binds to TLR1/2 and stimulates production of matrix metalloproteinase 9

A variety of Mycobacterium tuberculosis cell wall components induce expression of matrix metalloproteinase 9 (MMP-9) by monocytic cells and levels of MMP-9 in vivo positively correlate with severity of disease. Toll-like receptor (TLR)2 mediates cellular responses to acylated molecules but can also mediate responsiveness to diverse molecular structures, including non-acylated native viral and bacterial proteins. MPT/B-83 is a cell-associated lipoglycoprotein common to M. tuberculosis and M. bovis and an important antigen during infection of cattle. Since MPB83 is acylated and glycosylated, we investigated whether MPB83 would induce MMP-9 expression via interaction with TLR2, and assessed the contribution of the lipid, glycan and polypeptide components to its activity. Acylated peptide derived from MPB83 stimulated MMP-9 expression by human macrophage cells via interaction with both TLR2 and TLR1, but not TLR4. Lesser induction was found with secreted (non-acylated, but glycosylated) MPB83 protein purified from culture of M. bovis. Stimulation of cells with MPB83 induced TNF-α production which acted to upregulate MMP-9 expression. Surprisingly, recombinant MPB83 protein devoid of any post-translational modification also induced MMP-9 expression. Direct interaction of RecMPB83 with TLR2 was demonstrated by surface plasmon-resonance. MPB83 may act as a virulence factor through TLR2 mediated induction of MMP-9.

Pattern of matrix metalloproteinases-9, P53 and BCL-2 proteins in Egyptian patients with pulmonary Mycobacterium tuberculosis

Matrix metalloproteinases (MMPs) constitute a large family of enzymes that degrade extracellular matrix proteins (ECM). MMPs are implicated in different pathological conditions such as cancer. Bcl-2 and P53 are key controllers of programmed cell death (PCD) or apoptosis. The aim of the present study was to determine the MMP-9, P53 and Bcl-2 levels in Egyptian patients with Mycobacterium tuberculosis (MTB) (Group I) compared with healthy control individuals (Group II). The concentrations of serum MMP-9 were determined quantitatively using enzyme immunoassay (EIA). P53 and Bcl-2 levels were assayed by flow cytometric analysis using specific monoclones. MMP-9 level was significantly higher in MTB patients compared with healthy control. Similarly, P53 and Bcl-2 levels were increased in MTB patients compared with healthy ones. These data reflect the alteration of MMP-9 level during the course of MTB infection, accompanied with apparent dysregulation of cellular apoptosis as indicated by P53 and Bcl-2 over-expression.

Mycobacterium tuberculosis upregulates microglial matrix metalloproteinase-1 and -3 expression and secretion via NF-kappaB- and Activator Protein-1-dependent monocyte networks

Inflammatory tissue destruction is central to pathology in CNS tuberculosis (TB). We hypothesized that microglial-derived matrix metalloproteinases (MMPs) have a key role in driving such damage. Analysis of all of the MMPs demonstrated that conditioned medium from Mycobacterium tuberculosis-infected human monocytes (CoMTb) stimulated greater MMP-1, -3, and -9 gene expression in human microglial cells than direct infection. In patients with CNS TB, MMP-1/-3 immunoreactivity was demonstrated in the center of brain granulomas. Concurrently, CoMTb decreased expression of the inhibitors, tissue inhibitor of metalloproteinase-2, -3, and -4. MMP-1/-3 secretion was significantly inhibited by dexamethasone, which reduces mortality in CNS TB. Surface-enhanced laser desorption ionization time-of-flight analysis of CoMTb showed that TNF-alpha and IL-1beta are necessary but not sufficient for upregulating MMP-1 secretion and act synergistically to drive MMP-3 secretion. Chemical inhibition and promoter-reporter analyses showed that NF-kappaB and AP-1 c-Jun/FosB heterodimers regulate CoMTb-induced MMP-1/-3 secretion. Furthermore, NF-kappaB p65 and AP-1 c-Jun subunits were upregulated in biopsy granulomas from patients with cerebral TB. In summary, functionally unopposed, network-dependent microglial MMP-1/-3 gene expression and secretion regulated by NF-kappaB and AP-1 subunits were demonstrated in vitro and, for the first time, in CNS TB patients. Dexamethasone suppression of MMP-1/-3 gene expression provides a novel mechanism explaining the benefit of steroid therapy in these patients.

Influence of bovine lactoferrin on expression of presentation molecules on BCG-infected bone marrow derived macrophages

The current vaccine for tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is an attenuated strain of Mycobacterium bovis bacillus Calmette-Guerin (BCG). BCG has proven to be effective in children, however, efficacy wanes in adulthood. Lactoferrin, a natural protein with immunomodulatory properties, is a potential adjuvant candidate to enhance efficacy of BCG. These studies define bovine lactoferrin as an enhancer of the BCG vaccine, functioning in part by modulating macrophage ability to present antigen and stimulate T-cells. BCG-infected bone marrow derived macrophages (BMMs) cultured with bovine lactoferrin increased the number of MHC II(+) expressing cells. Addition of IFN-gamma and lactoferrin to BCG-infected BMMs enhanced MHC II expressiona dna increased the ratio of CD86/CD80. Lactoferrin treated BCG-infected BMMs were able to stimulate an increase in IFN-gamma production from presensitized CD3(+) splenocytes. Together, these results demonstrate that bovine lactoferrin is capable of modulating BCG-infected macrophages to enhance T-cell stimulation through increased surface expression of antigen presentation and co-stimulatory molecules, which potentially explains the observed in vivo bovine lactoferrin enhancement of BCG vaccine efficacy to protect against virulent MTB infection.

Synergistic up-regulation of epithelial cell matrix metalloproteinase-9 secretion in tuberculosis

Mycobacterium tuberculosis (MTb) kills approximately 2 million people each year. MTb must drive host tissue destruction to disseminate and also to cause pulmonary cavitation. Matrix metalloproteinase-9 (MMP-9, gelatinase B) is implicated in this Tb-related immunopathology. We demonstrate that conditioned media from MTb-infected monocytes (CoMTb), but not direct infection with MTb, up-regulates MMP-9 gene expression and secretion from primary human bronchial epithelial cells (NHBE). MMP-9 secretion was increased 8.7-fold by CoMTb (P < 0.05) as assayed by gelatin zymography. A549 and 16HBE14o epithelial cell MMP secretion was significantly less than primary NHBE secretion. MMP-9 secretion was decreased 53.2% by inhibition of the p38 mitogen-activated protein kinase (MAPK) by SB203580 (P < 0.01) and 48.3% by inhibition of extracellular signal-regulated kinase with PD98059 (P < 0.05). MMP-9 secretion was prostaglandin independent. TNF-alpha was necessary but not sufficient for MMP-9 up-regulation by the monocyte-epithelial cell network. Soluble factors derived from Tb culture synergized with TNF-alpha to increase MMP-9 secretion by NHBE 6-fold (P < 0.01 compared with either stimulus alone). Together, these data reveal a new mechanism by which host- and pathogen-derived factors act together in MTb infection to drive MAPK-dependent MMP-9 secretion from respiratory epithelial cells.

Modulation of gamma interferon receptor 1 by Mycobacterium tuberculosis: a potential immune response evasive mechanism

Mycobacterium tuberculosis inhibits gamma interferon (IFN-gamma)-mediated antimycobacterial action by adopting diverse mechanisms. IFN-gamma binds to its receptor, IFN-gammaR, in order to initiate proper signaling. We have observed reduced surface expression levels of IFN-gamma receptor 1 (IFN-gammaR1) in untreated pulmonary tuberculosis patients compared to those in healthy individuals (P < 0.01). Following antitubercular therapy, the expression of IFN-gammaR1 was restored in these patients. To delineate the mechanism by which M. tuberculosis modulates IFN-gammaR1, in vitro experiments were designed, wherein the down modulation of IFN-gammaR1 surface expression was observed for CD14+ cells in peripheral blood mononuclear cells (PBMCs) cocultured with live M. tuberculosis compared to that for uninfected cells (P < 0.01). No modulation of IFN-gammaR1 expression was observed for CD14+ cells in PBMCs infected with Mycobacterium smegmatis. A time-dependent decrease in IFN-gammaR1 mRNA expression was observed for PBMCs infected with M. tuberculosis. Similar down modulation of IFN-gammaR1 protein and mRNA expression in phorbol myristate acetate-differentiated THP-1 cells (pdTHP-1) by M. tuberculosis was observed (P < 0.01). Using reporter gene analysis of 5' deletion constructs of the IFN-gammaR1 gene (IFNGR1) promoter, the decrease in IFN-gammaR1 mRNA in M. tuberculosis-infected pdTHP-1 cells was shown to be due to the decreased transcription of IFNGR1. By immunoblotting and electrophoretic mobility shift assays, the down regulation of stimulating protein 1 (Sp1) expression and its recruitment on the phorbol ester-responsive element of the IFNGR1 promoter in M. tuberculosis-infected pdTHP-1 cells was observed. This down regulation of Sp1 in pdTHP-1 cells cocultured with M. tuberculosis may be responsible for the down regulation of IFN-gammaR1 expression, thereby potentially altering its receptivity to IFN-gamma.

Identification by surface plasmon resonance of the mycobacterial lipomannan and lipoarabinomannan domains involved in binding to CD14 and LPS-binding protein

The mycobacterial lipoglycans, lipomannan (LM) and lipoarabinomannan (LAM), regulate host defence mechanisms through their interaction with pattern recognition receptors such as Toll-like receptors (TLRs). We have developed a surface plasmon resonance assay to analyse the molecular basis for the recognition of Mycobacterium kansasii LM or LAM, by immobilized CD14 and LPS-binding protein (LBP) both being capable to promote presentation of bacterial glycolipids to TLRs. The affinity of either LM/LAM was higher to CD14 than to LBP. Kinetic and Scatchard analyses were consistent with a model involving a single class of binding sites. These interactions required the lipidic anchor, but not the carbohydrate domains, of LM or LAM. We also provide evidence that addition of recombinant LBP enhanced the stimulatory effect of LM or LAM on matrix metalloproteinase-9 expression and secretion in macrophages, through a TLR1/TLR2-dependent mechanism.

Matrix metalloproteinases in lung: multiple, multifarious, and multifaceted

The matrix metalloproteinases (MMPs), a family of 25 secreted and cell surface-bound neutral proteinases, process a large array of extracellular and cell surface proteins under normal and pathological conditions. MMPs play critical roles in lung organogenesis, but their expression, for the most part, is downregulated after generation of the alveoli. Our knowledge about the resurgence of the MMPs that occurs in most inflammatory diseases of the lung is rapidly expanding. Although not all members of the MMP family are found within the lung tissue, many are upregulated during the acute and chronic phases of these diseases. Furthermore, potential MMP targets in the lung include all structural proteins in the extracellular matrix (ECM), cell adhesion molecules, growth factors, cytokines, and chemokines. However, what is less known is the role of MMP proteolysis in modulating the function of these substrates in vivo. Because of their multiplicity and substantial substrate overlap, MMPs are thought to have redundant functions. However, as we explore in this review, such redundancy most likely evolved as a necessary compensatory mechanism given the critical regulatory importance of MMPs. While inhibition of MMPs has been proposed as a therapeutic option in a variety of inflammatory lung conditions, a complete understanding of the biology of these complex enzymes is needed before we can reasonably consider them as therapeutic targets.

Matrix metalloproteinases in destructive pulmonary pathology

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that have a number of important physiological roles including remodelling of the extracellular matrix, facilitating cell migration, cleaving cytokines, and activating defensins. However, excess MMP activity may lead to tissue destruction. The biology of MMP and the role of these proteases in normal pulmonary immunity are reviewed, and evidence that implicates excess MMP activity in causing matrix breakdown in chronic obstructive pulmonary disease (COPD), acute respiratory distress syndrome (ARDS), sarcoidosis, and tuberculosis is discussed. Evidence from both clinical studies and animal models showing that stromal and inflammatory cell MMP expression leads to immunopathology is examined, and the mechanisms by which excess MMP activity may be targeted to improve clinical outcomes are discussed.

Mycobacterial lipomannan induces matrix metalloproteinase-9 expression in human macrophagic cells through a Toll-like receptor 1 (TLR1)/TLR2- and CD14-dependent mechanism

Lipomannans (LM) from various mycobacterial species were found to induce expression and secretion of the matrix metalloproteinase 9 (MMP-9) both in human macrophage-like differentiated THP-1 cells and in primary human macrophages. Inhibition studies using antireceptor-neutralizing antibodies are indicative of a Toll-like receptor 1 (TLR1)/TLR2- and CD14-dependent signaling mechanism. Moreover, LM was shown to down-regulate transcription of the metalloproteinase inhibitor TIMP-1, a major endogenous MMP-9 regulator.

The 19-kDa antigen of Mycobacterium tuberculosis is a major adhesin that binds the mannose receptor of THP-1 monocytic cells and promotes phagocytosis of mycobacteria

Identification of mycobacterial adhesins is needed to understand better the pathogenesis of tuberculosis and to develop new strategies to fight this infection. In this work, THP-1 monocytic cells were incubated with Mycobacterium tuberculosis culture filtrate proteins labelled with biotin and a dominant 19-kDa adhesin was found. This adhesin was characterized as the glycosylated and acylated 19-kDa antigen (Rv 3763). These findings were confirmed in assays with culture filtrate proteins and cell-wall fractions from a recombinant Mycobacterium smegmatis strain that overexpresses the 19-kDa antigen. Further, fluorescent microspheres coated with recombinant culture filtrate proteins adhere to cells in higher numbers than microspheres coated with native M. smegmatis proteins. The binding of the 19-kDa antigen to cells was inhibited with mannose receptor competitor sugars, Ca(2+) chelators and with a monoclonal antibody to the human mannose receptor. Phagocytosis assays showed high-level binding of bacilli to THP-1 cells that was inhibited with alpha-methyl-mannoside, mannan, EDTA and mAbs to the mannose receptor and to the 19-kDa M. tuberculosis antigen. Immunoprecipitation, cell-surface ELISA and immunostaining confirmed the expression of the mannose receptor by THP-1 cells. In conclusion, here we show that the macrophage mannose receptor, considered a pathogen pattern recognition receptor, may interact with mannose residues of mycobacterial glycoproteins that could promote the phagocytosis of mycobacteria.

Mycobacterium tuberculosis, but not vaccine BCG, specifically upregulates matrix metalloproteinase-1

RATIONALE

Pulmonary cavitation is fundamental to the global success of Mycobacterium tuberculosis. However, the mechanisms of this lung destruction are poorly understood. The biochemistry of lung matrix predicts matrix metalloproteinase (MMP) involvement in immunopathology.

METHODS

We investigated gene expression of all MMPs, proteins with a disintegrin and metalloproteinase domain, and tissue inhibitors of metalloproteinases in M. tuberculosis-infected human macrophages by real-time polymerase chain reaction. MMP secretion was measured by zymography and Western analysis, and expression in patients with pulmonary tuberculosis was localized by immunohistochemistry.

RESULTS

MMP-1 and MMP-7 gene expression and secretion are potently upregulated by M. tuberculosis, and no increase in tissue inhibitor of metalloproteinase expression occurs to oppose their activity. Dexamethasone completely suppresses MMP-1 but not MMP-7 gene expression and secretion. In patients with active tuberculosis, macrophages express MMP-1 and MMP-7 adjacent to areas of tissue destruction. MMP-1 but not MMP-7 expression and secretion are relatively M. tuberculosis specific, are not upregulated by tuberculosis-associated cytokines, and are prostaglandin dependent. In contrast, the vaccine M. bovis bacillus Calmette-Guérin (BCG) does not stimulate MMP-1 secretion from human macrophages, although M. tuberculosis and BCG do upregulate MMP-7 equally. BCG-infected macrophages secrete reduced prostaglandin E2 concentrations compared with M. tuberculosis-infected macrophages, and prostaglandin pathway supplementation augments MMP-1 secretion from BCG-infected cells.

CONCLUSIONS

M. tuberculosis specifically upregulates MMP-1 in a cellular model of human infection and in patients with tuberculosis. In contrast, vaccine BCG, which does not cause lung cavitation, does not upregulate prostaglandin E2-dependent MMP-1 secretion.

Expression of matrix metalloproteinase-9 in pleural effusions of tuberculosis and lung cancer

BACKGROUND

Matrix metalloproteinase (MMP)-9 has been implicated in the development of pleural effusions.

OBJECTIVES

The aim of this study was to assess the expression of MMP-9 in pleural effusions of tuberculosis, lung cancer and transudates.

METHODS

Ninety-one patients (37 tuberculous pleural effusions, 42 malignant pleural effusions of lung cancer and 12 transudates) were included. Concentrations of pleural fluid MMP-9 and tissue inhibitors of matrix metalloproteinase (TIMP)-1 were determined by immunoassay. We also investigated the cellular localization of MMP-9 and TIMP-1 by reverse-transcriptase polymerase chain reaction on lymphocytes from pleural effusions and by immunohistochemical analysis of pleural tissues.

RESULTS

Pleural fluid MMP-9 levels, MMP-9/total protein and MMP-9/TIMP-1 ratios were significantly higher in tuberculous pleural effusions, whilst TIMP-1 levels were similar in the three groups. MMP-9 levels positively correlated with TIMP-1 and lactate dehydrogenase levels, and negatively with pH and glucose levels in pleural effusions. MMP-9 mRNA expression in lymphocytes tended to be higher in malignant pleural effusions of lung cancer than in the other groups without reaching statistical significance. The strongest immunoreactivity for MMP-9 was observed in epithelioid cells of tuberculous pleural tissues. Much lower levels of MMP-9 expression were found in tumor cells of pleural tissues.

CONCLUSIONS

MMP-9 is increased in tuberculous pleural effusions compared with transudates and malignant pleural effusions of lung cancer and is produced predominantly by epithelioid cells in the granulomas of tuberculous pleural tissues.

HIV-1 interaction with human mannose receptor (hMR) induces production of matrix metalloproteinase 2 (MMP-2) through hMR-mediated intracellular signaling in astrocytes

Astrocytes are susceptible to HIV-1 infection. We have recently demonstrated that human mannose receptor (hMR) is directly involved in CD4-independent HIV-1 infection of astrocytes. The apparent paradox between the vivid binding affinity of HIV-1 gp120 protein to hMR and the low efficiency of hMR-mediated HIV-1 infection raises the possibility that HIV-1 binding to hMR alone may negatively affect astrocyte function. In this study, we examined the relationship between HIV-1 interaction with hMR and the production of matrix metalloproteinases (MMPs) in astrocytes. We took advantage of an astroglial cell line U87.MR stably expressing hMR as an in vitro astrocyte model system and human primary astrocytes, and demonstrated that HIV-1 binding to astrocytes induced the production of MMP-2. This induction appeared to be most potent with M-tropic HIV-1 viruses. Increased MMP-2 production was not due to hMR-mediated HIV-1 entry and/or HIV-1 viral gene expression, as the transfection of HIV-1 proviral DNA did not result in MMP-2 production, and the infection of AT-2-treated HIV-1 viruses did not inhibit MMP-2 production. Direct involvement of hMR in HIV-induced MMP-2 production was confirmed by the inhibition of the yeast mannan, an hMR ligand antagonist, and an anti-hMR serum. Furthermore, HIV-induced MMP-2 production in astrocytes was shown to involve hMR-mediated intracellular signaling. Taken together, these results suggest that HIV-1 binding to astrocytes in the absence of HIV-1 viral entry is sufficient to alter astrocyte function through hMR-mediated intracellular signaling. In addition, these results provide new evidence to support the notion that hMR is capable of eliciting intracellular signaling upon ligand binding.

The presence of functional mannose receptor on macrophages at the maternal-fetal interface

BACKGROUND

The mannose receptor (MR) is involved in the initiation of the immune response and regulation of homeostasis during inflammation and tissue remodeling.

METHODS

Distribution, endocytosis and possible natural ligand tumor associated glycoprotein-72 (TAG-72) for the MR have been examined by immunohistology, immunocytochemistry and flow cytometry at the maternal-fetal interface, characterized by extensive tissue remodeling.

RESULTS

Contrary to disseminated distribution of the MR positive (MR+) cells in term placenta, the MR+ cells of early pregnancy decidua intimately surrounded glands and followed tissue distribution of CD14 positive cells. The mannose receptor was present on freshly isolated first trimester decidual mononuclear cells and distributed mostly on macrophages (77.08 +/- 10.55%, mean +/- SD). The expression of the MR on CD14 positive cells decreased following 18 h culture (P < 0.01) and was accompanied by the reduction of fluorescein isothiocyanate (FITC)-dextran uptake. PAM-1 anti-MR antibody, mannan and TAG-72 reduced FITC-dextran uptake by decidual macrophages.

CONCLUSIONS

These data indicate that the MR+ macrophages, surrounding early decidual glands, are able to internalize ligands for carbohydrate recognition domain of the receptor, including decidual secretory phase mucin TAG-72.

The down-regulation of cathepsin G in THP-1 monocytes after infection with Mycobacterium tuberculosis is associated with increased intracellular survival of bacilli

Cathepsin G (CatG) is a serine protease found in the azurophilic granules of monocytes that is known to have antimicrobial properties, but its role in Mycobacterium tuberculosis infection is unknown. We found that M. tuberculosis infection of human THP-1 monocytic cells induced the down-regulation of CatG mRNA expression, as demonstrated by gene array analysis and reverse transcription-PCR. This was associated with a concomitant decrease in CatG protein and enzymatic activity. In contrast, the expression of lysosomal cathepsins B and D was up-regulated in infected cells. This effect was also observed when THP-1 cells were induced to differentiate into adherent macrophages by exposure to bacterial lipopolysaccharide (LPS). In agreement with this, CatG expression was null in adherent macrophages isolated from bronchoalveolar lavages and normal blood. We wanted to determine if the down-regulation of CatG would be relevant to M. tuberculosis infection. First, we found that addition of CatG to THP-1 cells prior to infection resulted in decreased bacillary viability, presumably due to extracellular killing of bacilli. However, pretreatment of cells with LPS, which decreases intracellular CatG expression, resulted in increased bacillary viability. Second, we found that CatG cationic peptides killed M. tuberculosis bacilli and were five- to sevenfold more bactericidal than full-length CatG. These observations suggest that M. tuberculosis infection of human monocytic cells results in a "cathepsin switch" with down-regulation of CatG rendering M. tuberculosis bacilli more viable. Therefore, the down-regulation of CatG in macrophages is advantageous to M. tuberculosis bacilli and possibly is an important mechanism by which M. tuberculosis is able to evade the host immune defenses.

Transforming growth factor-beta1, myofibroblasts, and tissue remodeling in the pathogenesis of tracheal injury: potential role of gastroesophageal reflux

Subglottic stenosis (SGS) is characterized by the obliteration of the tracheal lumen due to excessive deposition of connective tissue. We hypothesize that tracheal injury triggers the early production of transforming growth factor-beta1 (TGF-beta1), a factor implicated in fibroproliferative disorders. In turn, TGF-beta1 stimulates the transformation of tracheal fibroblasts into myofibroblasts with increased matrix production and scar contraction that might be influential in laying the foundation for the development of SGS. Consistent with this hypothesis, histologic analysis of tracheas from humans with SGS and from rats with experimental tracheal injury revealed increased alpha-smooth muscle actin-positive cells as compared to control tracheas, suggesting increased myofibroblast differentiation. Rat tracheal fibroblasts exposed to TGF-beta1 or gastric juice in vitro showed increased expression of alpha-smooth muscle actin, alterations in the expression of matrix molecules, and increased contraction of collagen gels. These findings suggest that gastric juice or other agents of tracheal injury promote tissue remodeling through the stimulation of the differentiation of fibroblasts into myofibroblasts.

CD4-independent infection of astrocytes by human immunodeficiency virus type 1: requirement for the human mannose receptor

Human immunodeficiency virus type 1 (HIV-1) infection occurs in the central nervous system and causes a variety of neurobehavioral and neuropathological disorders. Both microglia, the residential macrophages in the brain, and astrocytes are susceptible to HIV-1 infection. Unlike microglia that express and utilize CD4 and chemokine coreceptors CCR5 and CCR3 for HIV-1 infection, astrocytes fail to express CD4. Astrocytes express several chemokine coreceptors; however, the involvement of these receptors in astrocyte HIV-1 infection appears to be insignificant. In the present study using an expression cloning strategy, the cDNA for the human mannose receptor (hMR) was found to be essential for CD4-independent HIV-1 infectivity. Ectopic expression of functional hMR rendered U87.MG astrocytic cells susceptible to HIV-1 infection, whereas anti-hMR serum and hMR-specific siRNA blocked HIV-1 infection in human primary astrocytes. In agreement with these findings, hMR bound to HIV-1 virions via the abundant and highly mannosylated sugar moieties of HIV-1 envelope glycoprotein gp120 in a Ca(2+)-dependent fashion. Moreover, hMR-mediated HIV-1 infection was dependent upon endocytic trafficking as assessed by transmission electron microscopy, as well as inhibition of viral entry by endosomo- and lysosomotropic drugs. Taken together, these results demonstrate the direct involvement of hMR in HIV-1 infection of astrocytes and suggest that HIV-1 interaction with hMR plays an important role in HIV-1 neuropathogenesis.

Regulation of monocyte chemokine and MMP-9 secretion by proinflammatory cytokines in tuberculous osteomyelitis

Tuberculous osteomyelitis causes bony destruction as a result of interactions among the pathogen, resident bone cells, and influxing leukocytes. Recruitment of monocytes and T cells is critical for antimycobacterial granuloma formation, but little is known about mechanisms regulating this in bone. We investigated the role of tumor necrosis factor alpha (TNF-alpha) and interleukin (IL)-1, key cytokines in granuloma formation, in networks involving human osteoblasts and monocytes. Experiments focused on CXC ligand (CXCL)8, CCL2, and matrix metalloproteinase (MMP)-9, human monocyte-derived mediators involved in control of leukocyte influx. TNF-alpha but not IL-1 has a key role stimulating CXCL8 secretion in Mycobacterium tuberculosis-infected human osteoblast MG-63 cells. Conditioned medium from M. tuberculosis-infected osteoblasts (COBTB) drives CXCL8 and some CCL2 gene expression and secretion from primary human monocytes. IL-1 receptor antagonist and to a lesser extent anti-TNF-alpha inhibited COBTB-induced CXCL8 secretion (P<0.01) but did not affect gene expression. IL-1 blockade had a comparatively lesser effect on CCL2 secretion, whereas anti-TNF decreased CCL2 concentrations from 7840 +/- 140 to 360 +/- 80 pg/ml/4 x 10(5) cells. Neither proinflammatory mediator affects MMP-9 secretion from COBTB-stimulated human monocytes. In summary, in a paracrine network, M. tuberculosis-infected osteoblasts drive high-level CXCL8, comparatively less CCL2, but do not alter MMP-9 secretion from uninfected human monocytes. This network is, in part, regulated by IL-1 and TNF-alpha.

Gene expression profiling detects patterns of human macrophage responses following Mycobacterium tuberculosis infection

High-density oligonucleotide microarrays allow simultaneous monitoring of the expression of a large number of cellular genes. Microarrays were used to screen the global human monocyte-derived macrophage transcriptional response to infection with the intracellular pathogen Mycobacterium tuberculosis. The microarray detected reproducible patterns of regulated gene expression. Analysis of the expression data showed induction of cytokines and chemokines, ribosomal proteins, and the interferon-response gene Stat1. Several changes were validated by quantitative reverse transcription polymerase chain reaction and immunoblot assays. Augmentation of the respiratory burst and preservation of the response to interferon-gamma were also demonstrated. These data supplement existing knowledge on macrophage responses to tuberculosis infection.

MyD88 primes macrophages for full-scale activation by interferon-gamma yet mediates few responses to Mycobacterium tuberculosis

Macrophages are activated from a resting state by a combination of cytokines and microbial products. Microbes are often sensed through Toll-like receptors signaling through MyD88. We used large-scale microarrays in multiple replicate experiments followed by stringent statistical analysis to compare gene expression in wild-type (WT) and MyD88^−/− macrophages. We confirmed key results by quantitative reverse transcription polymerase chain reaction, Western blot, and enzyme-linked immunosorbent assay. Surprisingly, many genes, such as inducible nitric oxide synthase, IRG-1, IP-10, MIG, RANTES, and interleukin 6 were induced by interferon (IFN)-γ from 5- to 100-fold less extensively in MyD88^−/− macrophages than in WT macrophages. Thus, widespread, full-scale activation of macrophages by IFN-γ requires MyD88. Analysis of the mechanism revealed that MyD88 mediates a process of self-priming by which resting macrophages produce a low level of tumor necrosis factor. This and other factors lead to basal activation of nuclear factor κB, which synergizes with IFN-γ for gene induction. In contrast, infection by live, virulent Mycobacterium tuberculosis (Mtb) activated macrophages largely through MyD88-independent pathways, and macrophages did not need MyD88 to kill Mtb in vitro. Thus, MyD88 plays a dynamic role in resting macrophages that supports IFN-γ–dependent activation, whereas macrophages can respond to a complex microbial stimulus, the tubercle bacillus, chiefly by other routes.